phenomen a book

The world changed, all the people of the world got a "system" making them be like RPG characters, but this "system" that brought emotion and happiness also brought with it an apocalypse of monsters, zombies, mutants. To fight against this apocalypse humanity had to use the "system" and become stronger, but this also brought the true face of humanity "The strong eats the weak and the weak is eaten" the world lost its morale and is a all against all.